Preflattened corox unit



394a A. BARNSTEHNER 2,208,405

PREFLATTENED COROX UNIT Filed Nov. 30, 1937 2 Sheets-Sheet 1 WITNESSES:

INVENTOR f7? 5. fl/fozzs Barns/amen ATTORNEY y 6, 1949- A. BARNSTEKNER 2 ,405

PREFLATTENED COROX UNIT Filed Nov. 50, 1937 2 Sheets-Sheet 2 WITNESSES: 32 INVENTOR 507$ 4/72/75 fiar/frsie/zait BY i ATTORNEY Patented July 16, 194-0 UNITED STATES PATENT OFFICE PREFLATTENED COROX UNIT Pennsylvania Application November 30, 1937, Serial No. 177,312

2 Claims.

My invention relates to heating units, and more particularly, to electric range surface units adapted for relatively quick heating.

With those metal-covered surface units now g, known to the art in which magnesium oxide has generally been used for insulation, it has been the practice in some cases to deform or alter the cross-section of the tube or unit, such as by flattening, so that the insulating material around the heating member will be compressed, it being the object of such procedure to compact the insulating' material into as dense or solid a mass as possible. In producing surface units in which there is formed a sharp angular bend within the surface sheets or plates, it has been necessary to anneal or normalize such unit so as to relieve the internal stresses set up within the sheets or plates due to such deformation. It is, therefore, an object of my invention to provide means for preducing a range surface unit in which the plates may be deformed in any manner desired and in which an insulating material, such as magnesium oxide or the like will satisfactorily function Without the need of normalizing or annealing the plates.

In one type of prior art surface unit it has been customary to convert magnesium metal into magnesium oxide by the use of steam or water at high temperatures and pressures, and the subsequent application of heat. These units were then deformed or flattened so as to reduce the cross-section of the space in which the magnesium oxide was contained. However, in some cases as the cross-section of such space was di- 35 minished or altered, the magnesium oxide crystals were broken and the path of heat conduction between the resistance member and the oxide walls of the retaining member was altered. It, therefore, was necessary to further flatten or deform the cross-section of such member so as to further break or pulverize the magnesium oxide crystals and to compress such pulverized magnesium oxide to form a solid, dense mass of material. It is apparent that should sufiicient alteration or compress the magnesium oxide in such manner 5, formed. container in which the magnesium oxide,

deformation of the container be performed to crystals are retained in their original condition and still proper heat conduction and dielectric strength are obtained.

It is a further object of my invention to provide a range surface unit of high efficiency which will be capable of withstanding severe shocks and strains on the upper surface thereof and which will have an exceptionally long life.

A further object of my invention is to provide a range surface unit from which there will be a uniform heat distribution.

A still further object of my invention is to provide means for reducing the heating element and insulation temperature while providing a desirably high cooking temperature.

Other objects of my invention will either be pointed out specifically in the course of the following description of a device embodying my invention, or will be apparent from such description.

In the accompanyin sheets of drawings:

Figure 1 is a top view of a device embodying my invention;

Fig. 2 is a sectional view taken along the line II-II of Fig. 1;

Fig. 3 is an enlarged fragmentary view similar to Fig. 2;

Fig. 4 is a view taken along the line IV-IV of Fig. l of a preferred form of a top plate;

Fig. 5 is a bottom view of a device embodying my invention in its final form;

Figs. 6 and 7 are enlarged partial sectional views taken along the lines VIVI and VII-V11, respectively, of Fig. 5, showing the device in its preliminary form; and

Fig. 8 is a partial sectional view similar to Fig. 3, showing the surface unit in one of its stages of manufacture.

Like reference characters indicate like parts in the several figures.

Referring to the accompanying drawings, I show a range surface unit or heating unit HI having atop plate H, a bottom plate !4, and a resistance element It insulatedly mounted between the top plate and bottom plate. Each plate has two interlacing spiral grooves therein as hereinafter more fully set forth, the grooves in the top plate being in alignment with the grooves in the lower plate so that the resistance elements and spiral casings of insulationmay be disposed therein. The top plate l2 has two interlacing spiral grooves it formed therein. These grooves have substantially fiat tops and are formed in such manner that there will be sharp corners 28 between the grooves l8 and the surface plate l2. Thus the grooves l 8 may be preformed in the top sheet l2 to provide the heating contact area and general shape desired in the finished surface unit. However, while forming the grooves E8 in the plate I2, considerable internal stresses and strains will be set up therein at points corresponding to the sharp corners 20 and 22. The top sheet l2 may then be normalized or annealed in such a manner that these internal stresses and strains will be diminished. It is, therefore, ap parent that with the internal strains removed from the top plate l2, after such top platehas been combined with the bottom plate It to form the surface units H], such surface unit it will not have to be annealed or normalized a sec- 0nd time.

The bottom plate It is preformed to produce grooves 24 having a rounded bottom. It is to be understood that the point at which the grooves 2% meet the main surface of the bottom sheet M will provide. sharp corners as hereinabove described with respect to the top sheets l2. Additional flattened V-shaped grooves 28, as shown in Figs. 5 and 7, may be formed within the bottom sheet M so as to join adjacent whorls of the grooves 24. However, it is to be understood that the grooves 28 need not be V-shaped, although some form of groove is required in the bottom plate for the reasons hereinafter described. Likewise, ears 30 (Fig. 6) should be bent in the outer edge of the bottom sheet l4 substantially radially in line with the V-shaped grooves 28.

It is to be understood that as the grooves 24 and 28 and the ears 30 are formed within the bottom plate It, substantial internal stresses and strains will be. produced within thebottom sheet, and it is preferred that such sheet be annealed or normalized to relieve such stresses before being united with the top plate l2 to form the surface unit I.

In making the range surface unit 10 using top plates l2 and M, which have thus been preformed and normalized or annealed to relieve their internal stresses and strains, the bottom plate M is located substantially beneath the top plate I2 in such a manner that the grooves 24 will be in line or cooperate with the grooves I8 of the top plate.

-The cooperating grooves I8 and 24 will then produce two hollow spaces or spiral passages 32 as shown in the sectional view of Fig.2. The resistance element "5, preferably helical in form, and a quantity of magnesium 33,preferably in the form of a ribbon placed around or within the resistance element, or both, are located within the hollow spaces 32, after which the top plate I2 is placed upon the bottom plate 14 as shown in Fig. 8. The depending portions 34 (Fig. 4) of the top plate l2 are then bent inwardly against the bottom plate I4 so as to tightly hold it against the top plate l2 as shown at 36 in Fig. 2.

The unit comprising the top plate I2, bottom plate [4 with the resistance element [6 and the magnesium ribbon 32 located within the hollow spaces 32, as above described, is placed preferably within an autoclave and subjected to steam or water at a high temperature and pressure. Such treatment converts the magnesium metal into magnesium hydroxide, which expands so as to fill the hollow space 32 with a dense insulating material. The resistance element It, due to its being located within and about the magnesium metal, will be suspended substantially in the center of the hollow spaces 32 as it becomes filled with the magnesium hydroxide.

The unit I0 is then subjected to a sufficiently high temperature during a predetermined length of time to expel the moisture in the magnesium hydroxide, which in turn leaves a clear, dense compact mass of magnesium oxide crystals. The magnesium oxide crystals 38 are in intimate relationship between the resistance element is and the inner walls of the hollow spaces 32. In fact,

it has been found from experiment that the,

greater percentage of these crystals will be in intimate contact with the resistance element at one end and the sides of the hollow space 32, substantially as shown in Fig. 3. The additional crystals then fill that space which is not occupied by those crystals which extend between the resistance member and the side walls of the hollow space. It is, therefore, obvious that the crystals 38 will then form a heat conducting and electric insulating medium with respect to the resistance element l6.

As such high temperature is supplied to the heating unit either through the resistance element 16 itself, or through an additional source, the moisture within the magnesium hydroxide will be converted into steam or vapor. If no means were provided for this steam or vapor to expel itself other than through the open ends of the hollow space 32, there would be the possibility of such steam or vapor increasing in pressure to such an extent that it would deform or bulge the unit in. The V-shaped grooves 28 located between the adjacent whorls of the hollow space 32 permit this steam or vapor to proceed along such grooves, located in a radial line, and to expel to the atmosphere through the depending portion or ears 30.

As the crystals 38 are formed within the hollow spaces 32, as hereinabove described, the resistance element I6 will be positioned relatively close to the top surface of each of the hollow spaces 32. This uneven positioning of the resistance element I6 will occur because of the crystals, located above the member, swelling out into the corners 39; which in turn reduce the number of crystals directly above the resistance element it. More effective coil area will, therefore, be brought close to the operating surface of the surface unit, ensuring an efiicient unit which will come up to its red heat within a very short time after being connected to a supply circuit, not shown. However, the inherent compactness of the magnesium oxide crystals will provide a sufficiently high dielectric strength between the resistance element 16 and the top wall of the unit.

The foregoing heat and pressure treatments of the unit are known to the art and constitute no part of my present invention.

Due to the inherent characteristics of the magnesium oxide crystals, the heat developed in the finished unit by the resistance element [6 will be uniformly distributed therefrom and, further, due to its high heat conductivity, will rapidly conduct the heat from such element to the walls of the hollow space 32. It is further obvious that due to the rapid conduction of heat from the resistance element It to the walls of the hollow space 32, the temperature of the resistance element and of the insulation material itself will be substantially reduced with respect to former units, and, that since the resistance element is located closer to the top of the hollow space 32, more heat will be conducted upwardly and the temperature of such top plate will be greatly increased over the remainder of the hollow space 32.

After the magnesium metal has been changed to the magnesium oxide crystals in the manner hereinabove described, the plates l2 and M are rigidly attached together Without deforming or altering the cross-section of the hollow spaces 32 in any manner whatsoever. It is preferred that the two plates be spot-welded together substantially by introducing a sufficient pressure and. current to the V-shaped grooves 28, whereupon such grooves will be deformed into a sub stantially fiat surface and the two plates will be Welded together as shown at 40 in Fig. 2. The ears 3!! will likewise be biased upwardly so as to contactfthe top plate l2, permitting the depending portions 34 to be rigidly pressed against such plate, holding it against the top plate l2. If it be desired, the ears 3!! may be spot welded against the top plate l2 as it is being pressed against it substantially as shown at "32 in Fig. 2.

If it be desired, a bolt 44 may be positioned within a central aperture 45 in the bottom plate l4 before the unit I0 is assembled, whereupon the head 48 of the bolt M will hold such bolt rigidly within the aperture 46. With the bolt M rigidly attached to the unit Iii in such a manner, it is obvious that such bolt may be used to attach the surface unit to any desired supporting frame.

It will be seen that I have thus provided a rugged quick-heating unit for surface cooking, which provides ample fiat contact surfaces without necessitating deformation and normalizing of the metal casing after assembly.

Various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims.

I claim as my invention:

v1. The method of manufacturing a heating unit having a top plate, a bottom plate and an insulated heating element therebetween, which method includes forming cooperating grooves in the plates, the groove in the top plate having a flattened portion whereby a relatively large contact surface is defined on the top of the plate for receiving a cooking utensil, annealing the plates to remove internal stresses and strains produced therein during the formation of the grooves, inserting a resistance element and magnesium metal between the plates Within the cooperating grooves subsequent to said annealing operation, then treating the assembled unit with fluid under high pressure and temperature to convert the magnesium metal into crystallized material, removing moisture from the crystallized material and then rigidly attaching the plates together without deforming or'altering the condition of the crystallized material, all of the recited steps subsequent to the annealing step providing substantially no annealing effect on the plates.

2. The method of manufacturing a heating unit having a top plate, a bottom plate and an insulated heating element therebetween, which method includes forming a flattened groove in the top plate only, annealing said plates so as to remove internal stresses and strains therein, and, subsequent to the annealing step, inserting a resistance element and magnesium metal between the plates and within said groove, treating the assembled unit with fluid under high pressure and temperature to convert the magnesium metal into magnesium oxide, treating the magnesium oxide with heat to convert it into a crystalline material, and rigidly attaching the plates together without deforming or altering the condition of the insulating material. all of the recited steps subsequent to the annealing step providing substantially no annealing effect on the plates.

ALFONS BARNS'I'EINER. 

